A structure of LSI has been recently getting finer along with larger scale integration and has become a multilayer structure where metal wirings are stacked in several layers on the surface of a semiconductor. And also, copper (Cu) which has lower electric resistance has been proposed to be used for the metal wiring, replacing conventional aluminum.
A process to form a multilayer structure using Cu wiring comprises forming grooves on an insulating film such as silicon oxide, then depositing metal copper on the whole surface of a semiconductor by a method such as plating and sputtering, subsequently polishing excess metal Cu by means of so-called chemical mechanical polishing technology (CMP), which is a technique to flatten a semiconductor substrate surface by mechanical polishing while oxidizing metal Cu with supply of slurry, which is dispersion of fine particles of metal oxide such as alumina and silica in aqueous solution, and oxidizing agent at the same time on a wafer surface, forming Cu wiring by planarization of the surface with Cu remained only in the grooves to complete wiring (Cu-CMP step), and repeating said process with planarization of each layer.
On the other hand, since the surface of a semiconductor after the Cu-CMP step is contaminated with impurities such as iron oxide and copper oxide (CuO) coming from Cu used for the wiring by oxidation, which may affect electrical properties of a semiconductor and destroy a device, and also particles derived from the slurry used, it is required to remove these impurities by cleaning without impairing metal Cu of wiring exposed on the same plane as the surface of a semiconductor after the Cu-CMP step, and silicon dioxide (SiO2) of interlayer dielectrics by introducing a cleaning step (post Cu-CMP cleaning) after the Cu-CMP step.
This post Cu-CMP cleaning is conventionally performed by chemical cleaning using an acidic cleaning agent such as HPM (hydrochloric acid-hydrogen peroxide type), DHF (diluted hydrofluoric acid type), a neutral cleaning agent such as buffered hydrofluoric acid, an alkaline cleaning agent such as APM (ammonia-hydrogen peroxide type), an organic acid type cleaning agent represented by citric acid, or the like, or physical cleaning using, for example, high-speed rotation brush made of polyvinylalcohol or high frequency or the like, or combination thereof.
However, in chemical cleaning, an acid type cleaning agent is insufficient in removing particles, although it has high ability to remove CuO, and highly acidic solution corrodes even Cu wiring. In addition, hydrofluoric acid type cleaning agent etches even SiO2 of interlayer dielectrics because the agent has characteristics to dissolve SiO2. Further, neutral and alkaline cleaning agent are generally insufficient in removing CuO due to their low ability to dissolve CuO, although they have high ability to remove particles without corroding Cu wiring.
On the other hand, physical cleaning is insufficient in removing CuO, while it can remove particles physically and does not corrode Cu wiring. Therefore, physical cleaning is generally used together with the above acid type cleaning agents. However, since the above problems caused by the acid type cleaning agent can not be avoided even in a combined use of physical cleaning and chemical cleaning agents, it is required to manage to use as weak as possible acid and to shorten cleaning period, and sometimes sufficient removal of CuO, particles can not be expected.
Thus, an effective mean is not presently available by which both CuO and particles remaining on the surface of a semiconductor on which Cu wiring is provided can be removed at the same time by easy operation.
The present invention is completed considering such situations, and provides a cleaning agent and a method for cleaning the surface of a semiconductor on which copper wiring is provided.